This invention relates to a hydrogenation catalyst useful for treating aromatic and/or heterocyclic aromatic compounds-containing feed such as gas oils.
Exhaust gases from diesel engines contain particulates including soot, soluble organic fraction (SOF), sulfates and water. SOF contains a trace amount of various polycyclic aromatic compounds, such as benzo[a]pyrene, which are harmful to human bodies. Aromatic substances contained in gas oils are considered to be sources of such pollutants. Thus, there is a great demand for grade-up of gas oils, especially for reduction of aromatic and/or heterocyclic aromatic compounds therein.
In production of gas oils, a deep desulfurization treatment is generally carried out so that the sulfur content in the gas oil is maintained at 500 ppm or less. The deep desulfurization is usually performed at a high temperature and a high hydrogen pressure so as to compensate a reduction of catalytic performance with process time. However, an increase of the desulfurization temperature has a problem because hydrogenated products are apt to undergo dehydrogenation to form aromatic compounds. To cope with this problem, use of a platinum or palladium catalyst having a high hydrogenation activity under mild conditions has been proposed (for example, U.S. Pat. Nos. 4,640,764, 4,960,505, 5,391,291, 5,147,526, 5,151,172, 5,271,823 and 5,308,814, EP-B-0303332 and EP-A-0519573. Such a noble metal catalyst, however, causes a problem of poisoning by sulfur compounds.
In Collected Abstracts of Lecture for Presentation of Reports in the 26th Meeting of the Society of Petroleum/Petroleum Chemistry (1996), it is reported that a catalyst containing Pd and/or Pt supported on an ultrastable zeolite Y carrier can partly solve the problem of catalyst poisoning. JP-A-H9-239018 discloses a hydrogenation catalyst having an improved resistance to sulfur poisoning and containing Pd and Pt supported on a zeolite catalyst which has been modified with cerium, lanthanum, magnesium, calcium or strontium.
The known catalyst, however, has been found to be poisoned with sulfur when a basic nitrogen compound is present in the oil feed or when a basic nitrogen compound or ammonia is formed in situ during the hydrogenation treatment.
It is, therefore, an object of the present invention to provide a dehydrogenation catalyst which is devoid of the drawbacks of the conventional catalysts.
Another object of the present invention is to provide a dehydrogenation catalyst which exhibits a high hydrogenation activity, which is resistant to sulfur compounds and nitrogen compounds inclusive of ammonia and which has a long catalyst life.
It is a further object of the present invention to provide a process which can hydrogenate an aromatic and/or heterocyclic aromatic compounds-containing feed such as gas oils.
In accomplishing the foregoing objects, there is provided in accordance with the present invention a hydrogenation catalyst comprising a carrier of ultrastable zeolite Y modified with at least one heavy rare earth element selected from the group consisting of ytterbium, gadolinium, terbium and dysprosium, and at least one catalytic metal supported on said carrier and selected from the group consisting of palladium and platinum.
In another aspect, the present invention provides a process for hydrogenating a feed containing an aromatic and/or a heterocyclic aromatic compound, comprising contacting said feed with hydrogen in the presence of the above hydrogenation catalyst.
The present invention also provides a carrier comprising ultrastable zeolite Y modified with at least one heavy rare earth element selected from the group consisting of ytterbium, gadolinium, terbium and dysprosium.
As compared with a conventional Pd and Pt-supported, Ce-modified zeolite catalyst, which is known to have the highest hydrogenation activity among the known Pd and Pt-supported zeolite catalysts, the catalyst according to the present invention exhibits superior hydrogenation activity. Thus, the catalyst of the present invention can catalyze hydrogenation of aromatic or heteroaromatic compounds into aliphatic or heterocyclic rings, which may also be accompanied with cleavage of the rings. Yet, the catalyst of the present invention exhibits high resistance to poisoning by sulfur and nitrogen compounds contained in a raw material feed or formed in situ during the hydrogenation.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments to follow.
In the present invention, ultrastable zeolite Y modified with at least one heavy rare earth element is used as a carrier for supporting at least one catalytic metal component. xe2x80x9cUltrastable zeolite Yxe2x80x9d is well known in the art and described in, for example, U.S. Pat. Nos. 3,293,192 and 3,402,996 and the publication, Society of Chemical Engineering (London) Monograph Molecular Sieves, page 186 (1968), the teachings of which are hereby incorporated by reference herein. The ultrastable zeolite Y generally has a molar ratio of SiO2/Al2O3 of 5.0-1,000, preferably 10-20.
The ultrastable zeolite Y is modified with at least one heavy rare earth element selected from the group consisting of ytterbium (Yb), gadolinium (Gd), terbium (Tb) and dysprosium (Dy). The modification of the ultrastable zeolite Y with a heavy rare earth element may be achieved by ion exchange of proton of the zeolite Y with the heavy rare earth element or by impregnation of the zeolite Y with the heavy rare earth element. The amount of the heavy rate earth element in the carrier is generally 0.002-0.1 part by weight, preferably 0.01-0.5 part by weight, per part by weight of the ultrastable zeolite Y, when ion exchange is adopted for the modification of the zeolite Y. In the case of the impregnation, the amount of the heavy rate earth element is generally 0.005-0.7 part by weight, preferably 0.02-0.25 part by weight, per part by weight of the ultrastable zeolite Y.
Composited with or supported on the modified ultrastable zeolite Y carrier is at least one catalytic metal selected from palladium (Pd) and platinum (Pt). The support of the catalytic metal on the carrier may be achieved by, for example, impregnation. The catalytic metal component may be present as an elemental metal, a sulfide or a mixture thereof. If desired, one or more auxiliary metal components, such as rhodium (Rh), iridium (Ir) and rhenium (Re) may be additionally supported on the carrier by, for example, impregnation.
The amount of the catalytic metal is generally 0.3-7 parts by weight per 100 parts by weight of the carrier. More particularly, when palladium is used by itself as the catalytic metal component, suitable amount of palladium is 0.3-4 parts by weight, more preferably 0.7-1.6 parts by weight, per 100 parts by weight of the carrier. When platinum only is used, the amount thereof is preferably 0.3-7 parts by weight, more preferably 0.5-5 parts by weight, per 100 parts by weight of the carrier. When both palladium and platinum are used in combination, the amounts of the palladium and platinum are preferably 0.3-3.5 parts by weight and 0.2-1.6 parts by weight, respectively, per 100 parts by weight of the carrier, more preferably 0.7-1.4 parts by weight and 0.3-0.6 parts by weight, respectively, per 100 parts by weight of the carrier, with a total amount of the palladium and platinum being preferably 0.3-5 parts by weight, preferably 0.5-3 parts by weight, per 100 parts by weight of the carrier.
It is preferred that palladium and platinum be used together for reasons of obtaining very excellent resistance to catalytic poisoning. In this case, an atomic ratio Pd/Pt of the palladium to the platinum is preferably in the range of 9:1 to 1:1, more preferably 5:1 to 3:2. An atomic ratio M/(Pd+Pt) of the heavy rare earth element M to a total of the palladium and the platinum is preferably in the range of 16:1 to 1:5, more preferably 9:1 to 1:1.
The catalyst of the present invention which may be any desired shape such as powder, pellets, granules, a cylinder and a plate is useful for hydrogenating compounds having an aromatic or heteroaromatic ring. Examples of aromatic rings include a benzene ring, a naphthalene ring, an anthracene ring and a phenanthrene ring. Examples of heteroaromatic rings include a pyrrole ring, a furan ring, a benzofuran ring, a thionaphthene ring, a thiophene ring, an indole ring, an oxazole ring, a carbazole ring, a pyrane ring, a quinoline ring, an isoquinoline ring, picoline ring, a thiazole ring, a pyrazole ring, a pyridine ring, a toluidine ring, an acridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a phthalazine ring and a quinoxaline ring. It is without saying that the catalyst of the present invention is effective in hydrogenating various other compounds having groups capable of being hydrogenated, such as double bonds of cyclic compounds, olefinic double bonds, carbonyl groups and nitrile groups.
The catalyst of the present invention is particularly effective to hydrogenate hydrocarbon oils containing aromatic and/or heteroaromatic compounds, especially gas oils. Hydrogenation of a gas oil is preferably performed at a temperature of 250-350xc2x0 C., more preferably 270-330xc2x0 C. and a hydrogen partial pressure of 35-80 kg/cm2, more preferably 40-65 kg/cm2. By the hydrogenation treatment of the gas oil, not only an aromatic content thereof is reduced but also a sulfur content is decreased as a result of hydrogenation of aromatic groups in sulfur compounds.